Three times now my wife's Blazer 2003 4.3 would not start for her. Turns over but does not fire. I checked the fuel pump and pressure readings are 60psi and holds for 15 minute or longer. So I thought that it was not the fuel pump. But she does have the security light coming on and going off as she drives it. Could this be causing the starting problems? Last night it would not start so she took my truck I went out this morning and turned the motor over and it fired like there was no problem at all. This one really has me confused. Any suggestion would be appreciated.

 

sounds like it. The key gets worn and causes this issue. you can get a new cylinder with keys and change it yourself. Pretty simple job.